Functional Sites of Transfer RNA for the Binding to Messenger RNA-Ribosome Complex

Abstract

In order to understand the role of a common sequence -GpTpψpCpGp- in tRNA molecules, the inhibitory effects of the purified tetranucleotide TpψpCpGp were studied for aminoacyl-tRNA synthesis and for the aminoacyl-tRNA binding to mRNA-ribosome complex. Since TpψCpGp did not inhibit the aminoacylation of tRNA, it is unlikely that the TpψpCpGp sequence is involved in the functional sites of tRNA for an aminoacyl-tRNA synthetase. The tetranucleotide TpψpCpGp inhibited aminoacyl-tRNA binding to mRNA-ribosome complex. This inhibitory effect was weaker than the terminal-pCpCpA-free tRNA fragments. The inhibitory effect by the latter fragments was a little weaker than the terminal adenosine-oxidized tRNA or the non-aminoacylated tRNA, with which the binding of the aminoacyl-tRNA was inhibited competitively. These results suggested that in addition to and anticodon sequence and a 3′-terminal sequence-pCpCpA, the sequence TpψpCpGp is required for the aminoacyl-tRNA binding to the mRNA ribosome complex. It is further supported by the results of inhibition experiments with deaminated tRNA and with tRNA digested sequentially by phosphodiesterases [EC 3.1.4.1]. Partially deaminated tRNA inhibited the binding of Phe-tRNA to the poly U-ribosome complex, while it scarcely inhibited the binding of Lys-tRNA to the poly A-ribosome complex. This indicates that the specificity of the nucleotide sequence in the anticodon is required for matching tRNA to mRNA.